In the effort toward achieving higher data density on recording media, spin filters have become of interest for use in magnetoresistive (MR) read heads. FIG. 1 is a diagram of a conventional spin filter 10. In general, the conventional spin filter 10 would be incorporated into a MR read head (not explicitly shown), which would include leads electrically connected to other electronics to drive current through the conventional spin filter 10 during reading. In such an application, current is generally driven in the current perpendicular to the plane (CPP) configuration. The CPP configuration is in the z-direction depicted in FIG. 1.
The conventional spin filter 10 includes a seed layer 20, an antiferromagnetic (AFM) layer 30, a pinned layer 40, a nonmagnetic spacer layer 50, a free layer 60, a filter layer 70, a specular oxide layer 80, and a capping layer 90. The seed layer 20 is used to provide the appropriate surface for growing the AFM layer 30 with the desired crystal structure. The AFM layer 30 is used in pinning the magnetization of the pinned layer 40. The pinned layer 40 may be a synthetic pinned layer, including ferromagnetic layers 42 and 46 separated by an electrically conductive spacer layer 44 that is typically Ru. The electrically conductive spacer layer 44 has a thickness configured to ensure that the ferromagnetic layers 42 and 46 are antiferromagnetically coupled. Thus, the magnetization of the ferromagnetic layer 42 is pinned by the AFM layer 30. The magnetization of the ferromagnetic layer 46 is set because it is strongly antiferromagnetically coupled to the magnetization of the ferromagnetic layer 42. The nonmagnetic spacer layer 50 is typically electrically conductive, for example Cu. The free layer 60 is ferromagnetic and typically includes materials such as CoFe. The filter layer 80 has a high electrical conductivity and typically includes materials such as Cu. The specular oxide layer 80 may be a nano-oxide and typically includes materials such as alumina. The combination of the filter layer 70 and the specular oxide layer 80 ensures adequate specularity of scattering of electrons from the free layer 60 that are incident on the specular oxide layer 80. Consequently, the magnetoresistance of the conventional spin filter 10 is adequate. The capping layer 90 is typically oxidized Ta.
Although the conventional spin filter 10 functions, there are drawbacks to the use of the conventional spin filter 10. Insertion of the specular oxide layer 80 can increase the coercivity of the free layer 60, which is undesirable. Furthermore, the specular oxide layer 80 is generally a nano-oxide that can continue to oxidize during processing. The signal may degrade during the lifetime of the conventional spin filter 10. The conventional spin filter 10 thus suffers thermal instabilities and may have reduced reliability.
Analogous conventional spin filters are described in U.S. Pat. No. 6,795,279 B2; U.S. Pat. No. 6,556,390 B1; U.S. Pat. No. 5,898,612; U.S. Pat. No. 6,407,690 B1; U.S. Pat. No. 6,764,778 B2; U.S. Pat. No. 6,700,753 B2; U.S. Pat. No. 6,775,111 B2; U.S. Pat. No. 6,591,481; U.S. Pat. No. 6,613,380 B1; U.S. Pat. No. 6,636,398 B2.
Accordingly, what is needed is a system and method for providing a spin filter having improved thermal stability, signal sensitivity, and/or reliability.